The rate of attacks has quadrupled since the relative calm in the months before US forces pulled out in 2011.

Almost 1,000 were killed in Iraq during the past month alone, the UN has said, amid fears of a return to the sectarian conflict that peaked in 2008.

Most of the violence has been blamed on Sunni Islamist militants linked to al-Qaeda in Iraq (AQI), which belongs to the over-arching Islamic State in Iraq and the Levant (ISIS).

Iraq has also seen a spill-over of violence from the conflict in Syria, where jihadist rebels linked to the Islamic State of Iraq, a Sunni militant umbrella group that includes al-Qaeda, have risen to prominence.

In the past two months, Iraqi security forces have reportedly arrested hundreds of alleged al-Qaeda members in and around Baghdad as part of a campaign the government is calling "Revenge for the Martyrs".

But the operations, which have taken place mostly in Sunni districts, have angered the Sunni community and failed to halt the violence.